1. Field of the Invention
The present invention is related to providing an overheating prevention apparatus in a boiling clothes washing machine including a heater for laundering clothes with hot water, and a method thereof.
2. Related Art
A conventional fully automatic washing machine has been developed to provide a heating apparatus in the tub in order to process clothes with warm water having a temperature of about 50.degree. C. FIG. 1 illustrates a heater drive control circuit for the conventional washing machine. A microcomputer 10 controls all the operations of the washing machine according to a control program. A load drive section 20, which includes a first transistor 21 and a second transistor 22, outputs power supply switching signals to a power supply switching section 30 so as to control the operating cycles of the washing machine according to the control signal provided from the microcomputer 10. As far as the present invention is concerned, only the on/off operation of the heater 40 as controlled by the load drive section 20 will be described herein for brevity of explanation. The power supply switching section 30 includes a first relay 31 and a second relay 32 to connect or disconnect each terminal of the power supply with each corresponding terminal of the heater 40 according to the switching signal provided from the load drive section 20.
However, in the conventional washing machine as described above, there is the possibility that the clothes will become damaged or that a fire may take place if the power supply is applied to the heather 40 when there is an insufficient amount of the washing water in the tub.
An apparatus, supplied with a plurality of water level sensors and a thermostatic sensor to control the level and temperature of the washing water and also the quantity of detergent, is disclosed in U.S. Pat. No. 4,580,421. This apparatus is designed to automatically cut off the power supply to the heater 40 by operation of the thermostatic sensor when the temperature of the washing water reaches a predetermined value. One object of the disclosed device is to reduce the washing machine's consumption of electricity, water and detergent. But the U.S. patent does not disclose a definite means for preventing the heater from overheating or cutting off the power supply to the heater when the heater becomes overheated due to an insufficient amount of the washing water present in the tub. Thus, the risk of damage to the clothes and the risk of fire caused by the overheating of the heater still exists. Further, when terribly dirty clothes are boiled in washing water which is heated to around the boiling temperature, benefits (such as sterilization, deodorization and bleaching) are achieved. Such a boiling clothes washing machine requires an apparatus for preventing the heater from overheating which may be caused by an increase of power consumption at the heater.